Zippers and Twisters: Planes of Satellite Galaxies Emerge from Whirling and Shocking Gas Streams in the Cosmic Web

Abstract

We investigate dwarf satellite systems around Milky Way analogs in the NewHorizon simulation. Using simple estimators limiting over-detection, we identify planes of satellites comparable to observations in $30\%$ to $70\%$ of cases. The full sample is strongly biased towards arrangements more elongated and co-rotating than their dark-matter host, as early as $z = 1$. We identify cosmic filaments and relics of local gas streams outside each system at $z \approx 0$ with DisPerSE. We find that the thinner the local stream plane, the thinner the system is. The two align significantly for planar systems. Streams around isotropic systems are not planar. Our analysis reveals two plane types. Ultrathin planes lie orthogonally to their single nearest cosmic filament and align to coherent vortical flows within 3 Mpc, reminiscent of $z > 2$ whirls. A second group of planar systems align to their cosmic filaments. All planes are found in single cosmic filaments skirted by coherent vortical whirls while isotropic systems are found in turbulent flows at the intersection of filaments. We conclude that planes are frequent in $\Lambda CDM$ simulations providing the cosmic environment is resolved. Tracking filaments back in time, we show a tight connection between a single, stable filament down to $z \approx 0$ and the existence of a plane. "In-filament" planes typically get enhanced by a single, edge-on filament merger at $z < 2$ (zipper) while "vertical" planes' filaments undergo single twisters (high-orbital momentum zippers) preventing the formation of a core along the filament. In contrast, isotropic systems' filaments undergo multiple misaligned mergers.